The present disclosure relates to a semiconductor device having memory cells.
A storage device called a search memory or CAM (Content Addressable Memory) searches for a data word coincident with a search word from among data words stored in the storage device, and when a coincident data word is found, the storage device outputs an address of the coincident data word.
The CAM includes BCAM (Binary CAM) and TCAM (Ternary CAM). Each memory cell of the BCAM stores information of “0” or “1”. On the other hand, each memory cell of the TCAM can store information of “Don't Care” (in the present example, a symbol “*” is used for “Don't Care”) in addition to “0” and “1”. The symbol “*” indicates that any of “0” and “1” may be stored.
A TCAM device is widely used for address search and access control in a router for a network such as the Internet. To cope with increase in capacity, the TCAM device generally has a plurality of arrays, and a search operation is performed on each array at the same time.
The TCAM device can compare input search data (input packet) with TCAM cell data simultaneously, so that the TCAM device can perform the comparison quicker than when using a RAM (Random Access Memory) in all search usages.
Specifically, the TCAM device compares information stored in a memory cell with data which a user wants to search for, and a match line (ML) of the TCAM device indicates whether or not the information is coincident with the data.
Further, a configuration for outputting address information (Hit Index) corresponding to a match line indicating that the information is coincident with the data is provided (Japanese Unexamined Patent Application Publication No. 2013-101750).